It is conventionally believed that when a heel touches down on the ground, the shock applied to the heel is approximately 1.25 times higher than the human body weight during walking, and approximately three times higher than the human body weight during jogging. This shock is sequentially sent to the heel, an ankle, a knee, and hips.
Conventionally, a sole made of an elastic material is known as a shoe midsole for absorbing the shock applied when the heel touches down the ground. This elastic material absorbs the shock in the contacting area to the ground when the heel touches down on the ground.
Accordingly, the present applicant has proposed a technical means to spread and absorb the shock when the sole of a foot touches down on the ground during walking, and to stimulate the sole of a foot to be massaged (for example, see Patent Document 1).
Patent Document 1 disclosed that a fluid infused between a sole plate and a cover could spread and absorb the shock when the sole of a foot touched down on the ground, and could reduce a load on a knee, hips, etc. Patent Document 1 also disclosed the effect that the shock to the sole of a foot could be spread and absorbed with the fluid smoothly moved by uniformly tilting a plurality of blades toward the heel side, and the effect that the blades could massage the sole of a foot.
By the way, when we human being walk, we take a series of actions as follows: to contact with the ground as the first action, gradually contact a sole with the ground from the heel to the roots of toes as the next action, and to kick the ground with the toes as the last action. This series of actions is continuously repeated as one cycle of the actions.
Until now, it has been considered that the peak impact force is generated at the moment when the heel touches down on the ground within the one cycle of walking. However, it has been revealed that the impact force generated at the moment of kicking the ground of the roots of the toes is higher than the impact force generated at the moment of touchdown of heel on the ground as a simulation described later in FIG. 6.
However, according to the Patent Document 1 described above, the plurality of blades were uniformly tilted toward the heel side and it meant that the plurality of blades were same as the moving direction of the fluid at the moment of kicking the ground of the roots of the toes. Therefore, the fluid in the toe side is quickly moved to the heel side, and there is some risk, that the shock applied to the heel side is increased.
[Patent Document 1] U.S. Pat. No. 1,959,712 (Examined Patent Publication No. H6-91849)